U.S. Pat. No. 3,158,017 issued Nov. 24, 1964 entitled BURGLAR PROOF SAFE LOCKING BOLT ASSEMBLY is illustrative of a typical prior art safe door construction of the type with which the present invention is concerned. Basically, safe doors of the type shown and described in this prior patent comprise or are made up of a massive body provided with a circular recess defining an annular wall. Bolt guiding bores extend radially through this wall for receiving bolts. The bolts in turn may be retracted and extended by an appropriate cam plate received in the recess and arranged to rotate between first and second positions. The inner ends of the bolts are provided with grooves receiving the outer edge of the cam plate and appropriate cam slots are provided through which pins extending transversely of the grooves in the ends of the bolts pass to hold the bolts captive to the cam plate. The arrangement is such that all the bolts involved, normally three spaced at 120.degree., are simultaneously retracted or extended by rotation of the cam plate through a given circumferential distance; for example, 30.degree..
The cam plate itself is normally rotated between its locking and open positions by a cam driver member capable of being rotated in turn by the outer combination lock knob on the door when the proper combination has been worked. Thus, when the proper combination is carried out, a lever member is caused to effect engagement with a drive disc element secured to the end of a spindle shaft connecting to the combination knob. Rotation of the knob will thus rotate the cam plate driver and thereby rotate the cam plate to retract the bolts and open the door.
While safe doors as above described have worked fairly well, there is still room for ample improvement. A major problem involved is the construction of the safe door in such a manner as to minimize the possibility of successful burglaries. In this latter respect, one of the most common means of burglarizing safes of the type described is to drill into a wall of the safe opposite the extending bolts and then attempt to drive the bolts radially inwardly as by an appropriate driving rod and sledge hammer. One prior art means for attempting to frustrate such action is illustrated in the aforementioned U.S. Pat. No. 3,158,017 wherein there is provided a triangular shaped plate member cooperating with the cam plate to distribute any inward force exerted on a bolt to the other two bolts involved thereby tending to drive these latter bolts outwardly. While there is no question that such construction makes it more difficult to force inwardly any one of the bolts, damage to the internal mechanism of the combination lock can occur even though the burglar may not be successful in forcing a bolt inwardly. First, because of the pin constructions coupling the bolts to the cam plate, the pins themselves tend to be sheared and while the triangular reinforcing plate may still prevent inward movement of the bolt, the shearing of the pins requires a complete overhauling of the safe at considerable expense.
Even more important is the fact that the combination lock components themselves normally disposed in the central portion of the recess are often severely damaged by simple wear and tear, dropping or banging the door against walls, or by intentional attempts to force one or more of the bolts radially inwardly. Such blows are transmitted to the combination lock components through the cam plate and can cause severe damage requiring complete replacement.
In addition to the foregoing problems associated with wear and possible burglaries of such safe doors, other problems exist in the simple operation itself of the safe door. For example, many prior art combination locks have fixed wheel post on which the tumblers or wheels for the combination lock rotate One consequence is that the pick-up pin on the driver disc can start to turn the first wheel or tumbler before the cooperating lever and fence assembly have cleared the gate in the wheel. The resulting condition is referred to as a "locked open" condition and can only be corrected by resetting the entire combination. Further, wear and friction occur in such locks utilizing a fixed wheel post, this friction occurring during the locking and unlocking movements of the drive plate, cam plate and so forth.
Another problem in conventional safe door operation is a tendency for the lever for the drive plate to hang up on the fence pin by friction. Such hang-up of the lever prevents it from dropping into the disc shaped driver connected to the combination knob spindle. This problem can be overcome by providing a positive rotational force to the tumbler post actuating cam lever assembly in a direction opposite to the rotational direction of the assembly required to open the bolts. The problem however is that the bolts will tend to return to their locked position once the dial knob is released. Thus, a user of the lock would be required to hold the knob in the unlocked position while attempting to open the safe door all of which is totally impractical and would not be acceptable in a proper safe door.
Still other problems with prior art safes involve general difficulty in the assembly and disassembly of various elements primarily because of the large number of elements involved and the requirement of special tools.